A concept of microendoscopy has been described for minimally invasive therapy in medicine. Small sizes of these devices can reduce anesthesia requirements and minimize tissue damage, opening up the possibility of safer intervention. Ultraminiature endoscopes may also give rise to new procedures, permitting diagnosis and microsurgery in previously inaccessible areas of the body. Previously, however, a widespread adoption of microendoscopy may be hampered by the poor image quality of current devices and the overall size of the endoscope and its associated microsurgical instrumentation. One of the objects of the present invention is to provide a new form of microendoscopically-guided therapy that overcomes these limitations.
Operative Fetoscopy.
Endoscopically-guided fetal surgery is one of the applications of microendoscopy.4,5 Indications for intervention can include congenital diaphragmatic hernia, lower urinary tract obstruction, sacrococcygeal teratoma, and thoracic space occupying lesions, among others.5,6 Placental surgery, notably laser coagulation of vessels on the chorionic plate, has gained significant attention for the treatment of twin-twin transfusion syndrome (TTTS).7-13 The use of these techniques can result in live, healthy births in cases that would otherwise result in in utero fetal demise (IUFD).
Twin-Twin Transfusion Syndrome.
TTTS is considered a complication of monochorionic pregnancies where blood is preferentially shunted through placental arteriovenous (A-V) anastomoses towards one twin and away from the other. In severe TTTS, the donor twin becomes hypovolemic, resulting in oligohydramnios and oliguria.2 The recipient twin conversely becomes hemodynamically overloaded, with subsequent polyhydramnios and polyuria.2 Severe TTTS can occur in 15% of monochrorionic pregnancies, at a rate of approximately 3000/year in the United States.2 When left untreated, organ and cardiac failure ensue, resulting in mortality rates ranging from 80-90%, with significant neurological defects in surviving twins.2,14 
Laser Coagulation for Treatment of TTTS.
A variety of treatments for TTTS have been investigated, including serial amnioreduction, septostomy, and fetoscopically-guided laser coagulation of placental A-V anastomoses.2-4,15 Studies have shown that laser coagulation of communicating vessels appears to be the most promising of these techniques.3,15 Laser coagulation therapy of TTTS can use a microendoscope, containing an instrumentation port, which is inserted through a cannula into the amnionic cavity. Generally, the amniotic fluid is replaced with warmed, sterile normal saline or Hartmann's solution to facilitate visualization.1 Placental A-V anastomoses may be identified using the fetoscope by their characteristic anatomy, which can comprises an artery from one twin and a vein from the other, diving through a common foramen in the chorionic plate (as shown in FIG. 1A).16 A 100-400 μm optical fiber is then inserted into the accessory port. The anastomotic vessels are coagulated using 0.1 sec pulses of 40-100 W light provided by a diode or Nd:YAG laser (1064 nm) delivered through the optical fiber (see FIG. 1B).1 Multiple trials have shown that fetal survival is significantly improved when the laser coagulation is conducted prior to 26 weeks gestation, with an overall survival rate ranging from 55-72%.2,3,7 
Potential Issues with Laser Coagulation.
While overall survival is significantly improved with laser coagulation, acute fetal loss due to an iatrogenic preterm premature rupture of membranes (iPPROM) can occur in greater than about 10% of cases.4,12,17 This difficulty can be referred to as the “Achilles heel” of fetoscopic surgery.1,4,5 One of the primary factors implicated in this high rate of fatal complications is the size of currently available fetoscopically-guided surgical instrumentation.1,4,5 Conventional fetoscopes may have a diameter of 2.0 mm (see Karl Storz model 11630) and with the optical fiber for therapy, generally uses a 3.3 mm trocar for insertion into the amniotic sac.3 In comparison, 22-gauge amniocentesis needles (˜0.71 mm outer diameter) are generally associated with an iPPROM and fetal loss rate of <1%.18-21 The size of current instrumentation should be significantly reduced to avoid the unacceptably high complication rates associated with the use of current fetoscopy technology.1,4,5. 
Other than iPPROM, improvements in identifying culprit vessels can decrease the number of adverse perinatal outcomes following therapy. Recent studies have shown that in many laser coagulation cases with neonatal hematologic complications, recurrent TTTS, IUFD, and adverse neurological outcomes, culprit vessels were not identified fetoscopically, and the coagulation of communicating vessels was incomplete.22-25 The use of complementary procedures for visualizing blood flow, such as Doppler ultrasound,26-28 has recently been proposed to increase knowledge of the pathophysiology of TTTS and potentially provide additional diagnostic parameters to guide the therapeutic procedure. Additionally, development of further fetoscope technology can be beneficial to provide higher quality images and new diagnostic information. Progress in these areas will undoubtedly increase the probability of identifying more communicating vessels, which in turn would likely increase the efficacy of laser coagulation therapy.
Microendoscope Technology.
Fetoscopes can be constructed from fiber-optic imaging bundles, which transmit two-dimensional images from the amnionic cavity to the physician.1-3,5 Maintaining a good image quality with small diameter bundles is challenging; each optical fiber including its cladding has a finite diameter and only a limited number of optical fibers can be packed into a confined space. Small-diameter fiber bundles therefore provide images with a relatively low number of pixels. Single-mode fiber bundles, containing ultrathin fibers, have the highest fiber density. However these bundles are quite rigid and tend to have relatively low light throughput due to the cladding required on the optical fibers. Because the cladding does not transmit image data, pixelation artifact is also a problem, likely resulting in a honeycomb pattern superimposed on the image. The limitations of fiber bundles for miniature endoscopic imaging have motivated the search for other methods. Image formation with a single optical fiber is particularly attractive since single optical fibers are flexible and have excellent light transmission. There has been an attempt to rapidly scan light from a single fiber or the entire fiber itself to obtain an image.29-31 While images devoid of pixelation artifacts, have been obtained using these techniques, the size of the scanning mechanisms can prohibit their use in the smallest endoscopes.
Spectrally-Encoded Endoscopy.
Another exemplary procedure has been developed for microendoscopy, which can be identified as spectrally-encoded endoscopy (SEE).32 SEE can likely overcome the limitations of prior fiber-bundle fetoscopes for safer and more effective TTTS laser coagulation therapy. With SEE, e.g., a broadband light emanating from a fiber 200 can be separated into different colors (e.g., wavelengths) 210 using a lens/grating pair 220 at the distal end of the probe (as shown in FIG. 2). This exemplary optical configuration can focus each color onto a different location on the tissue, as illustrated in FIG. 2. Reflected light, returned back through the optics and fiber, can then be decoded outside of the body, using a spectrometer, to form one line of the endoscopic image. Such “fast-axis” of image acquisition can be performed remotely from the probe at rates ranging from 10-30 kHz. A two-dimensional image may be formed by moving the fiber using well-established mechanical devices, such as a motor or galvanometer that also reside outside the body.33 Such second, “slow-axis” of scanning can be performed at a 30 Hz video rate. Since a high-speed scanning mechanism is not needed inside the endoscope, the diameter of the SEE probe can be as small as that of the optical fiber, which can typically be sized in the range of 80-250 μm. Furthermore, the number of pixels in an SEE image can be larger than that of fiber bundles, dependent on the spectral width of the light source and the ability of the probe to separate out the different wavelength components.
Spectral encoding is not only provided for a two-dimensional endoscopy. For example, when the grating and lens are placed in one arm of an optical interferometer, such procedure can also provide depth information. Three-dimensional imaging can be obtained using spectral encoding with a variety of interferometric techniques, including. e.g., speckle pattern subtraction and time-domain heterodyne interferometry.34,35 